6. Abstract Almost 20 million people suffer from ischemic heart diseases in US and one million patients develop myocardial infarction (MI) every year. Many patients develop heart failure even if they survive the acute event, which clearly indicates that current interventions are not sufficient. Thus, the development of a new class of medicine, which prevents ischemia/reperfusion (I /R) injury, would have a large market opportunity and significant clinical advance. Cardiac myocyte death, including apoptosis, is intimately involved in the pathogenesis of heart failure. Mammalian sterile 20 like kinase 1 (Mst1) plays an important role in mediating cardiac myocyte apoptosis and is intimately involved in the pathogenesis of congestive heart failure (Vasade, US patent 7160859, 2007). Using transgenic mice with cardiac specific overexpression of dominant negative Mst1 (Tg-DN-Mst1), inhibition of endogenous Mst1 suppresses cardiac myocyte apoptosis in response to I/R, thereby reducing the size of MI and improving long-term cardiac function. One of the long-term goals of Vasade is to develop Mst1 specific inhibitors for the treatment of I/R injury. Through our effort made possible by the phase I STTR grant from NIH, Vasade 1) has discovered a novel and specific peptide Mst1 inhibitor (termed Mst1 inhibitory peptide 120 (MIP120)) and made it cell permeable (termed TAT120) and 2) has established an ELISA-based high throughput method to accurately determine the kinase activity of Mst1. To our knowledge, MIP120 and TAT120 are the only compounds currently available inhibiting the kinase activity of Mst1. In the phase II STTR project, Vasade will provide unequivocal evidence showing that the Mst1 inhibitor is useful for the prevention of cardiac myocyte death by I/R in vivo and identify a refined lead compound for the development of peptide mimetic Mst1 inhibitors for treatment of I/R injury. Specific aims are: Aim 1 To determine the effect of TAT120 on the size of MI and cardiac myocyte apoptosis in response to I/R in vivo, thereby establishing the proof of concept for the use of Mst1 inhibitors to reduce I/R injury using the mouse and pig models of ischemia/reperfusion. Aim 2 To further improve the property of MIP120 /TAT120 as Mst1 inhibitors and to elucidate the structure- function relationship of MIP120/TAT120 for the development of better peptides or peptide mimetics This phase II study will provide strong proof of concept and refined lead compounds, which will be used for the development of peptide mimetic small molecule Mst1 inhibitors for the future clinical treatment of I/R injury in the heart. PUBLIC HEALTH RELEVANCE: Almost 20 million people suffer from ischemic heart diseases in US and one million patients develop myocardial infarction (MI) every year. Many patients develop heart failure even if they survive the acute event, which clearly indicates that current interventions are not sufficient to prevent myocardial cell death and resultant left ventricular (LV) dysfunction. The current investigation is aiming at generating a new class of medicine preventing ischemia/reperfusion (I /R) injury, which should have a large market opportunity and significant clinical importance.